In the rat kidney immunoreactive kallikrein content was highest in the outer cortex and decreased progressively toward the papillary tip. In microdissected cortical nephron segments, the highest kallikrein content was found in the connecting tubule and in immediately adjacent segments. 2) Specific binding bradykinin to membrane preparations from homogenized cortex was higher than medulla. In microdissected nephron segments, significant binding was found in the length from the thick ascending limb to the collecting tubule. 3) "Urine" produced by the isolated perfused rat kidney contains kinin and kiniogen as well as kallikrein. 4) While the immunoreactive kallikrein levels of rat renal lymph appear to be similar to that in thoracic lymph, renin levels are 400-fold those of thoracic lymph. In contrast renal lymph contains about one-tenth as much angiotensin converting enzyme as either plasma or thoracic lymph. Paradoxically, angiotensin I could not be detected in thoracic lymph whereas renal lymph contained significant levels. Renal lymph also contains kinin and kininogen.